1. Field of the Invention
The invention is based on a metering valve assembly and on a method for operating a metering valve assembly for metering fluids.
2. Description of the Prior Art
For reducing the nitrogen oxides contained in an exhaust gas of an internal combustion engine, a method for selective catalytic reduction has proved advantageous for engines that are operated with air excess. In this method, the nitrogen oxides together with ammonia are converted in a selective catalytic converter into nitrogen and water. The reducing agent needed for the catalytic conversion of the nitrogen oxides is carried in the vehicle in the form of an aqueous urea solution, instead of ammonia, from which solution the ammonia can be liberated by hydrolysis of the urea solution in whatever quantity is required for the conversion. However, it is problematic that depending on the urea concentration, the risk exits that the aqueous urea solution will freeze at certain temperatures.
From International Patent Disclosure WO 02/42616 A1, a metering valve for an aqueous urea solution is known in whose work chamber walls or elements which at least in part yield under pressure are provided and can compensate reversibly for a pressure occurring with ice formation in the work chamber.